Modeling Multiphase Effects in the Combustion of HMX and RDX

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have similar structures and burning rates. However, the burning-rate temperature sensitivity ( σpσp) is significantly different between RDX and HMX at low pressures. Recent efforts to mathematically model the steady-state combustion of RDX and HMX with detailed chemical kinetics in the gas phase and distributed decomposition in the condensed phase have succeeded in modeling burning rates at a specific initial temperature. However, all have underpredicted the σpσp trends of HMX at low pressure and have not differentiated the σpσp of RDX and HMX. RDX and HMX both burn with a thin multiphase surface of bubbles in liquid. A liquid-bubble submodel was developed to improve σpσp calculations. To predict the observed HMX σpσp values with the model, first, evaporation in the subsurface was limited near the gas/liquid surface. Second, the difference in surface temperature at different initial temperatures was adjusted to follow trends in experimental data. Third, the Marangoni effect was added to the calculation of the bubble velocities. For RDX, there was little change in the calculated σpσp values with the addition of the liquid-bubble submodel. [PUBLISHER ABSTRACT]